Ethanol production by hydrogenation of acetic acid and/or esters thereof is an alternative to fermentation from starchy materials or cellulosic materials. A hydrogen source is required for this ethanol production. U.S. Pat. No. 4,497,967 uses a substantially pure hydrogen source, which includes inert diluents such as carbon dioxide, nitrogen, and methane, for converting aliphatic acetates to ethanol. To obtain substantially pure hydrogen, the hydrogen must be purified from the other components, which typically includes carbon monoxide. Several processes are known to obtain hydrogen from syngas, i.e., a mixture of hydrogen and carbon monoxide. Cryogenic purification is widely used to separate syngas as described in U.S. Pat. Nos. 5,511,382, 4,756,730, and 4,242,875, the entire contents and disclosures of which are hereby incorporated by reference. Another hydrogen separation is described in US Pub. No. 2007/0003477 for purifying a gaseous flow containing at least hydrogen, carbon monoxide, a metal carbonyl, and at least one impurity selected from oxygen, and unsaturated hydrocarbons. One problem in producing pure hydrogen and carbon monoxide streams is that the energy intensive separation. The presence of additional gases, such as nitrogen and methane, may further increase the energy requirements for separation. Also, the complexity of the purification process is dependent on the desired purity of the carbon monoxide and hydrogen.
Ethanol production processes having integrated hydrogen separation techniques. EP2060553 describes a process for the conversion of a carbonaceous feedstock to ethanol, wherein the carbonaceous feedstock is first converted to ethanoic acid, which is then hydrogenated and converted into ethanol. At least part of the hydrogen stream emanates from the syngas generation procedure.
U.S. Pat. No. 8,502,001 describes a process for the conversion of ethanoic acid into ethanol by (a) introducing ethanoic acid and H2 into a primary hydrogenation unit in the presence of a precious metal-based catalyst to produce ethanol and ethyl ethanoate and (b) introducing ethyl ethanoate, from step (a), together with H2 into a secondary hydrogenation unit in the presence of a copper-based catalyst to produce ethanol. Ethanol from step (b) is recovered.
U.S. Pat. No. 8,080,693 describes a process for converting methanol to ethanol which comprises reacting methanol and carbon monoxide in the presence of a catalyst to produce a product comprising at least 25 mole % methyl acetate and, in some instances, acetic acid. The acetic acid then is reacted with at least one alcohol to produce at least one acetate selected from methyl acetate, ethyl acetate, and butyl acetate. The at least one acetate (if produced) and the methyl acetate produced as a result of reacting methanol and carbon monoxide then are hydrogenated to produce ethanol. Syngas may be produced from biomass to produce all or a portion of the methanol, hydrogen, and carbon monoxide requirements for the process. Carbon monoxide and hydrogen that are employed in the process are each obtained from syngas and may be separated using membranes.
EP0167300 discloses a process for the production of an aliphatic alcohol having at least two carbon atoms, preferably ethanol, from a carbonaceous feedstock, preferably natural gas, via an intermediate aliphatic alcohol having one less carbon atom, preferably methanol, via an intermediate compound containing the group CH3(CH2)nC(O)—, preferably acetic acid. The feedstock is reformed and the synthesis gas formed is separated, preferably by a PSA unit, into three different streams which are used in the three stage process, one of which streams is a pure hydrogen stream that is used for reacting the intermediate compound to form the desired aliphatic alcohol.
Therefore, a need remains for improving the hydrogen feed stream and increasing production of ethanol.